The present invention relates to a roller bearing, and more particularly to an improvement of seizure resistance characteristics based on roughness of an end surface of a roller.
A tapered roller bearing has a plurality of tapered rollers between an inner ring member and an outer ring member. The inner ring member is provided at its axially opposite ends with flanges (or ribs). The flanges have guide surfaces for guiding opposite end surfaces of a large-diameter side and a small-diameter side of the tapered rollers in a sliding contact manner. A contact portion between the flanges on the axially opposite ends of the inner ring member and the end surfaces of the large-diameter side and small-diameter side of the tapered rollers is lubricated with lubricant such as oil, grease or the like. Such end surfaces of the tapered rollers and the guide surfaces of the flanges of the inner ring member have different microscopic surface shapes depending upon polishing methods at the time of surface finishing. Such microscopic surface shapes will be explained with reference to FIG. 10. A reference numeral 4A denotes a large-diameter side end surface of the tapered rollers, and a reference numeral 8 denotes a guide surface in the flange of the inner ring member. The large-diameter side end surface 4A has a microscopic surface shape in which a large number of polished marks T1 formed by the surface finishing working are remained only in the circumferential direction of the large-diameter side end surface 4A. Polished marks T2 are also remained in the guide surface 8 of the inner ring member 3 only in the circumferential direction of the guide surface 8 likewise. Such polished marks are microscopic surface shapes obtained by rotating the tapered roller or the inner ring member around its axis in a constant direction and by polishing by a constant grindstone. In FIG. 10, a symbol A denotes a sliding contact portion between the large-diameter side end surface 4A of the tapered roller and the guide surface 8 of the inner ring member. In such a tapered roller bearing, it is desired to enhance the seizure resistance characteristics when a high load is applied by enhancing the retention ability of lubricant oil in a circumferential direction of the roller end surface.
According to a roller bearing of the present invention, a plurality of rollers is interposed between an inner ring member and an outer ring member, and a flange (or rib) having a guide surface for guiding an end surface of the roller in a sliding contact manner is provided at an end portion of at least one of the inner ring member and outer ring member in an axial direction. In the roller bearing, three-dimensional surface roughness of the end surface of the roller or the guide surface of the flange is defined to a value which satisfies conditional expressions of Saxe2x89xa60.1 xcexcm and 0.15 mxe2x89xa6Svkxe2x89xa60.30 xcexcm, where Sa is arithmetical average roughness based on roughness curve and Svk is reduced valley depth based on the Abbott-firestone curve (bearing curve).
An experiment of the present inventors shows that if the surface roughness of the roller end surface or the guide surface of the flange is defined as the above-described conditional expressions, the seizure resistance characteristics can largely be enhanced. Herein, a surface defined by the conditional expressions of Saxe2x89xa60.1 xcexcm and 0.15 xcexcmxe2x89xa6Svkxe2x89xa60.30 xcexcm is a surface in which valleys of predetermined depth are dispersed on a predetermined smooth surface, and it is possible to effectively enhance the reserving ability of lubricant oil between surfaces of members which relatively slide on each other.
The above-described arithmetical average roughness Sa indicates smoothness of a surface. If this Sa value is greater than 0.1 xcexcm, smooth sliding motion required by the relatively sliding portions of the roller bearing can not be maintained, friction of the relatively sliding portions becomes great (or increases) and the rotation torque becomes excessively great (or increases). As a result, seizure is prone to be generated when a high load is applied.
The above-described reduced valley depth Svk indicates a depth of valley which exists in the surface and affects the oil-retention ability. If this Svk value is smaller than 0.15 xcexcm, since the depth of the valleys measured from the smooth surface is small, it can not be the that the valleys are dispersed in the smooth surface, and sufficient lubricant oil-retention ability can not be exhibited. On the other hand, if the depth of the valleys from the smooth surface is greater than 0.3 xcexcm, the depth of the valley is excessively deep, and the smooth sliding motion required for the relatively sliding portions of the roller bearing is hindered on the contrary. When the depth of the valley is excessively deep, the Sa value also becomes greater than 0.1 xcexcm.
The state in which valleys are dispersed in the smooth surface means a state in which the number of valleys is not too much, and a plurality of valleys are not arranged in a constant direction, e.g., in the circumferential direction, the-radial direction and the like. When the number of valleys is excessively great, the Sa value becomes greater than 0.1 xcexcm.
When there is no valley in the smooth surface, the smooth surface and the valleys are assimilated into the same level and thus, the Svk value becomes smaller than 0.15 xcexcm. When valleys exist in the smooth surface but the number of the valleys is too small, there are many cases in which no valleys exist in a measuring location in the smooth surface and thus, the Svk measuring value tends to become smaller than 0.15 xcexcm. Therefore, it is possible to define the dispersion degree of valleys by defining the Sa and Svk in the above-described ranges.
A reason why a two-dimensional surface roughness parameter which is defined by the conventionally used JIS B 0601 or ISO 4287 etc., can not be used for defining the distinctive surface of the present invention will be explained below. As described above, the surface of the present invention is characterized in that valleys having predetermined depth are disposed in the predetermined smooth surface. It is necessary to define the surface shape by reliably detecting and correctly quantifying the dispersed valleys irrespective of the measuring locations on the surface, and irrespective of directions of the valleys. Here, If a profile on one straight line is measured for defining such a surface using the conventional two-dimensional surface roughness parameter, valleys exist or do not exist depending upon the measuring locations. The profile of the surface largely differs between a case in which a direction of a length of the valley and a direction of the measuring straight line coincide with each other and a case in which they do not coincide with each other, and the roughness parameter value also largely differs. Therefore, even if the member""s surface is the same, the two-dimensional surface roughness parameter largely differs depending upon the measuring locations and measuring direction. That is, variation in measured values is large depending upon the microscopic shape of a surface, and it is extremely difficult to correctly define the microscopic shape of the surface.
As described above, a plurality of dispersed valleys of the invention are not aligned in a constant direction. Therefore, when the surface roughness is to be measured, the surface profile largely differs depending upon the measuring locations and the measuring direction, and it is difficult to define the microscopic shape of the surface. The three-dimensional surface roughness parameter including the Sa and Svk is a parameter which is obtained by a three-dimensional surface shape within a predetermined flat surface region not by a surface profile on a straight line. Therefore, when specific shapes such as valleys exist (are dispersed) on a surface at intervals of some degree or less, it is possible to substantially reliably detect the specific shapes, and to quantify the number, the size and the like of the specific shapes. For this reason, the three-dimensional surface roughness parameter was applied in the present invention.
A reason why the Sa and Svk are selected from a large number of three-dimensional surface roughness parameters is that the Sa and Svk are optimal for defining the microscopic surface shape which is distinctive for the present invention in which valleys are dispersed on a predetermined flat surface. It is described in Japanese Patent Application Laid-open No. 2000-205275 that a three-dimensional surface roughness parameter is effective and necessary for defining such a special surface in terms of quantification. The valley in this invention means a stripe shaped valley, not a dot-like valley.